The invention relates to power systems and more specifically to a system and method for controlling power.
Electric sources may be connected or organized in a network to enable the transmission of power to various devices, or communication between the devices. Such a network of interconnected devices may be described as a grid. For example, a power grid may be an interconnected network for delivering electricity from one or more power generators to the connected devices (e.g., customers of the utility company). A power grid may transmit AC power at a frequency, amplitude, and/or phase angle to a large number of electrical devices. Synchronized operation of a grid, or portions of a grid, may enable a pooling of power generation, as well as a pooling of loads to result in lower operating costs.
Though transmitting synchronized AC power may be beneficial to the efficient transmission and/or distribution of power, many factors may disturb the synchronization of a grid. For example, a power grid including an unbalanced power source may disturb the synchronization of the grid.
Typically, phase lock loops (PLLs) are used in power systems for synchronization. PLLs under balanced conditions generate a signal that has a fixed relation to the phase of an input signal. PLLs respond to both the frequency and the phase of the input signals, automatically raising or lowering the frequency of a controlled oscillator until it is matched to the reference in both frequency and phase. However, PLLs have limited success when employed in grids having unbalanced power sources.
Therefore there is a need to implement a control system that synchronizes the input power signals to the grid output signals.